A. Tick (œ“) the correct option:
1. Sound can travel through:
(a) gases only
(b) solids only
(c) liquids only
(d) solids, liquids and gases
2. Voice of which of the following is likely to have minimum frequency?
(a) Baby girl
(b) Baby boy
(c) A man
(d) A woman
3. Sound waves travel fastest in:
(a) air
(b) metals
(c) vacuum
(d) liquids
4. Sounds having frequency less than 20 Hz are called:
(a) supersonic
(b) ultrasonic
(c) sonar
(d) infrasonic
5. A tuning fork of frequency 384 Hz produces a lower note than one of frequency:
(a) 256 Hz
(b) 512 Hz
(c) 288 Hz
(d) 320 Hz
B. State True or False:
1. Sound cannot travel in vacuum. …………………
2. The number of oscillations per second of a vibrating object is called its time period. ……………..
3. If the amplitude of vibration is large, sound is feeble. ………………….
4. For human ears, the audible range is 20 Hz to 20,000 Hz. ………………..
5. The lower the frequency of vibration, the higher is the pitch. ……………..
6. Unwanted or unpleasant sound is termed as music. ……………..
7. Noise pollution may cause partial hearing impairment. ………………..
C. Fill in the blanks:
1. Time taken by an object to complete one oscillation is called ……………… .
2. Loudness is determined by the ………………. of vibration.
3. The unit of frequency is …………………. .
4. Unwanted sound is called ……………….. .
5. Shrillness of a sound is determined by the ………………. of vibration.
D. Answer the following questions in short:
1. A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
2. The sound from a mosquito is produced when it vibrates its wings at the average rate of 500 vibrations per second. What is the time period of the vibration?
3. Identify the part which vibrates to produce sound in the following instruments:
(a) Dholak
(b) Sitar
(c) Flute
4. What is the difference between noise and music? Can music become noise sometimes?
5. Explain in what way noise pollution is harmful to humans.
6. List sources of noise pollution in your surroundings.
7. Your parents are going to buy a house. They have been offered one on the roadside and another three lanes away from the roadside. Which house would you suggest your parents should buy? Explain your answer.
8. Sketch larynx and explain its function in your own words.
Answer:
9. Lightning and thunder take place in the sky at the same time and at the same distance from us. Lightning is seen earlier and thunder is heard later. Can you explain why?
10. How is sound produced and how is it transmitted and heard by us?
11. A child with a moderately severe hearing loss may have defective speech. Why?
E. Match the following:
| ‘A’ | ‘B’ |
| 1. High pitch sound | a. Frequency |
| 2. Number of vibrations produced by a vibrating particle in one second | b. Amplitude |
| 3. Flute | c. Time period |
| 4. Speed of sound in air | d. Frequency of vibration |
| 5. Sound propagation | e. Vacuum |
| 6. Time in which vibrating particle completes one vibration | f. 1000 Hz |
| 7. A medium through which sound cannot travel | g. 330 m/sec |
| 8. 1 kHz | h. Vibration |
| 9. Maximum displacement of a vibrating particle from its mean position | i. Material medium |
| 10. To and fro motion of a vibrating body about its mean position | j. Vibration air column |
| 11. Pitch | k. High frequency |
| 12. Loudness | l. Amplitude |
F. Prepare a list of famous Indian musicians and the instruments they play:
G. Make a list of familiar musical instruments and identify their vibrating parts. A few examples are given in the table. Complete the rest of the table:
